Sol−Gel Synthesis of Thick Ta₂O₅ Films

Abstract

Advances in microelectromechanical systems have generated an ever-growing demand for novel insulating material applicable to high-temperature systems. Ta2O5 is appealing for such applications because of its high index of refraction, refractory nature, and negligible absorbance in the infrared region. The challenge faced in the realization of such materials is the synthesis of crack-free Ta2O5 films whose thickness is on the order of a quarter wavelength of the incident infrared radiation. This work seeks to investigate the effect of addition of polyvinyl pyrollidone (PVP) as a binder material in the presence of 2-methoxyethanol and acetylacetone in the sol−gel synthesis of thick, uniform, and crack-free Ta2O5 films. Incorporation of PVP into the sol precursor has enabled uniform and crack-free films with thicknesses of up to 2.4 μm to be realized. Chemical probing of the precursor was conducted via TGA, FTIR, and NMR analysis of the sol to elucidate the processes behind this film formation, showing that the PVP hydrogen-bonds with the growing oxide but does not affect the sol chemistry. Instead, the PVP prevents crack formation, probably by relieving stresses in the film.